As defined herein, a "Subscriber" is a communication system user. "Subscriber traffic" is defined herein as data originating from one or more communication devices operated by one or more Subscribers. The Subscriber traffic-carrying capacity of a communications system is limited, because a finite quantity of resources (e.g., electrical energy stored in a satellite battery, or channel capacity of a radio link) exists within any communication system. Correspondingly, the number of Subscribers who may access the communication system at one time is also limited. When Subscriber traffic exceeds the capacity of the communication system, some Subscribers will be denied access. Frequent denial of access is likely to result in unsatisfied Subscribers.
In any system with finite resources, management of the system resources is desirable to provide better system performance (e.g., more Subscriber traffic-carrying capacity) than if resource management were not performed at all.
Prior art ground-based (non-cellular) communication systems (e.g., a telephone network) generally contain communication nodes (e.g., telephones or radios) utilized by Subscribers, a central control facility which manages overall operation of the system, and routing devices which route Subscriber traffic based on instructions from the central control facility. One function of the central control facility may be to control Subscriber traffic routing through the system. Prior art routing management may be done in a reactive manner (i.e., the control facility adjusts routing instructions in real-time by reacting to actual quantities of Subscriber traffic), or it may be done in a predictive manner (i.e., the control facility predicts future quantities of Subscriber traffic, and instructs routing devices to route future Subscriber traffic based on the prediction).
Prior art ground-based cellular communication systems also contain communication nodes (e.g., cellular telephones), routing devices, and a central control facility. However, central control facilities for prior art ground-based cellular communications systems do not manage Subscriber traffic routing in a predictive manner. They merely react to Subscriber traffic demand in real-time. When Subscriber traffic demand exceeds the capacity of the system, users will be denied access to the system.
Non-cellular and cellular routing devices typically have a fixed set of communication nodes to service. Non-cellular routing devices service communication nodes that are generally coupled to the specific routing device through some static transmission medium. Cellular routing devices service communication nodes that are located within a fixed geographical area within communication range of the particular routing device.
As communication needs grow, satellite cellular communication systems have become a desirable alternative to prior art ground-based non-cellular and cellular communication systems. Unlike prior art ground-based systems, satellite communication systems may readily provide world-wide communication coverage. Routing devices associated with satellite cellular communication systems (i.e., satellites) differ from routing devices of ground-based communication systems in two ways.
First, satellites may not service a fixed quantity of Subscribers. For non-geostationary satellites, the satellites move with respect to the surface of the earth. Thus, the geographical area, and the number of Subscribers seen by a satellite may vary dramatically with the changing location of the satellite.
Second, the resources of satellite cellular routing devices are highly dynamic. Weight and size constraints limit the quantity of resources each satellite may contain at launch. Additionally, resources are difficult to increase or replenish due to the remoteness of the satellites. For example, electrical energy replenishment may be accomplished by conversion of solar energy. This results in a cyclic state of charge of the satellite batteries because the satellite is only in a position to absorb solar energy when it is in view of the sun, or in twilight. When the earth is positioned between the satellite and the sun, the satellite cannot absorb solar energy. Because electrical energy is drained from the batteries as the satellite supplies on-board equipment and supports subscriber traffic, and electrical energy is replenished by the sun, the energy availability for the satellites is dynamic.
Accordingly, each satellite may have a completely different set of rules, and constraints from every other satellite, and the overall state of the system may never repeat. Ground-based routing devices, on the other hand, generally enjoy a continuous supply of energy, or energy is more easily replenished.
In a satellite communication system, resource management is critical because of the dynamic Subscriber traffic and the dynamic resource availability. Without resource management, for example, the electrical energy stored on board a satellite may rapidly be exhausted after the satellite passes into the shadow of the earth, and begins servicing Subscribers within a major metropolitan area. Service would then be denied to later Subscribers within the satellite's path until the satellite recharged its batteries. For example, a communication system should not allow Subscriber traffic from a busy metropolitan area (e.g., Tokyo, Japan) to consume all the stored energy on board a satellite that may be needed, say, ten minutes later to support another busy metropolitan area (e.g., Sydney, Australia).
Adequate resource management depends on an accurate prediction of Subscriber traffic which the satellite will encounter. Such a prediction would allow the communication system to knowledgeably limit Subscriber access over a particular metropolitan area while still providing acceptable service to the metropolitan area and other geographical areas over which the satellite subsequently passes.
What is needed is a method for predicting Subscriber traffic demand for a cellular communication system so that the resource use may be controlled in a manner which allows the system to handle Subscriber traffic efficiently. Particularly needed is a method for predicting Subscriber traffic demand for a satellite cellular communication system containing limited, dynamic resources, where Subscriber traffic demand varies.